Controlling method of forming thin film, system for said controlling method, exposure method and system for said exposure method

ABSTRACT

A method for irradiating a substrate such as a semiconductor substrate, coated with a photoresist, with light to measure variations in optical properties, such as reflectivity, refractive index, transmittance, polarization, spectral transmittance, for determining an optimum photoresist coating condition, an optimum photoresist baking condition, an optimum developing condition or an optimum exposure energy quantity, and forming a photoresist pattern according to the optimum condition. A system for the exposure method, a controlling method of forming a photoresist film by use of the exposure method, and a system for the controlling method, are useful for stabilization of the formation or treatment of the photoresist film, and ensure less variations in the pattern size. Furthermore, even in the case of a thin film other than a photoresist film, the formation or treatment of the thin film can be stabilized by measuring the optical property before and during or after the formation of the thin film and using the measurement results to control the condition for forming the thin film, the etching condition or the coating condition.

This is a continuation of co-pending application Ser. No. 594,351, filedon Oct. 9, 1990, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to the production of a semiconductordevice or the like, and more particularly to a controlling method forforming a thin film suitable for stabilization of formation or treatmentof a thin film of a semiconductor, a system for controlling the method,an exposure method and a system for the exposure method.

With the progress of high integration of semiconductor devices, patternsize has become finer, the device structure has becomethree-dimensional, and the manufacturing processes of semiconductordevices have become more complicated. It is therefore necessary to paymore attention than before to the stabilization of production processconditions in the manufacturing steps of semiconductor devices.

For instance, in projecting a pattern drawn on a reticle onto a wafer bya projection aligner, exposing light of a single wavelength in acomparatively narrow wavelength bandwidth is used. Therefore, as shownin FIG. 2a, the exposure light 71 undergoes multiple reflection in aphotoresist film 72 or in a light-transmitting undercoat forming film74. As a result, mutual interference of light occurs and the intensityof light varies in the depth direction inside the photoresist film 72.Accordingly, the exposure energy is varied in the depth direction and,upon development, the cross section of the photoresist film appearsrugged, as shown in FIG. 2b. When the process conditions in variousmanufacturing apparatuses are varied, the thickness of photoresist filmt or the formed condition of the light-transmitting undercoat 74 isvaried. Consequently, upon exposing a photoresist under the sameexposure energy, the width W of the photoresist in contact with theuppermost layer of the undercoat 73 is varied under the effect ofstationary waves, resulting in varied pattern size. In order tostabilize the pattern size W, an optimum exposure energy according tothe variation in the thickness of photoresist film t and the formedcondition of the undercoat 74 should be set.

When the optical property or thickness of the photoresist film is varieddue to variations in the photoresist coating or baking conditions in aphotoresist coating machine, the pattern size varies even if the formedcondition of the undercoat on the wafer or exposure and developingconditions are the same. It is therefore necessary, even in thephotoresist coating machine, to keep monitoring the variation in coatingand baking conditions, the major causes of variations in the thicknessand optical properties of the photoresist film.

In thin film forming and treating steps such as the film forming stepand etching step before or after the exposure step, as shown in FIG. 4,due to the increase in the diameter of the wafer formed and treated andthe decrease in the thickness of film, the thickness and opticalproperties of the thin film formed and treated are varied with slightvariations in the production process conditions. In a thin film formingand treating apparatus, therefore, it is necessary to constantly monitorthe thickness and optical properties of the thin film being formed ortreated, and to control the process conditions so as to keep constantthe thickness and optical properties of the thin film.

A preliminary operation method of maintaining a constant pattern sizein, for example, an exposure step in the presence of variations beenperformed in which exposure and development of one or several sheets ofwafer are conducted on a trial basis. The pattern size is measured by ameasuring instrument to judge the acceptability of exposure energy. Thejudgment is fed back to the opening and closing times for shutters in anoptical system for illumination, or the like.

In the manufacture of small volumes of many types of products such asASIC (Application Specific Integrated Circuit), however, the preliminaryoperation is required every time the type of product is changed. Therequirement has increased the number of working steps and has been themajor cause of lowering the operating efficiency of an exposureapparatus. With the trend towards higher integration, the method ofcorrecting variations in the process conditions by such preliminaryoperations is unable to give sufficient accuracy.

In order to eliminate the preliminary operations, a method has beendevised, as disclosed in Japanese Patent Application Laid-Open (KOKAI)No. 63-31116 (1988). In the method, assuming that the relationshipbetween the thickness of a photoresist film and pattern size and therelationship between exposure energy and pattern size are known, thethickness of a photoresist film on a wafer to be exposed is measured bya photoresist film thickness measuring apparatus incorporated in areduction projection aligner. The measurement result is fed back to theexposure energy so as to reduce variations in the pattern size and tostabilize the pattern size.

In a thin film-forming and treating step, also, a method has been usedin which the thickness of a photoresist film is measured for thepreceding wafer by an apparatus for forming and treating a thin film.The process conditions for fabrication of the intended product is setbased on the film thickness thus measured.

Of the prior arts mentioned above, the stabilization of pattern size hasbeen carried out by measuring variations of the thickness of aphotoresist film formed by coating, determining an optimum exposureenergy based on the measurement results, and controlling the patternsize. With the recent increasingly higher integration of semiconductordevices, however, it has become impossible to ignore the effects ofvariations in the manufacturing process conditions, such as variationsof the formed state of an undercoat due to variations in forming andtreating conditions in the thin film forming and treating step,variations of the optical properties of a photoresist film due tovariations in coating and baking conditions in the photoresist coatingstep, etc.

Furthermore, in the thin film forming and treating step according to theprior art, the operation with the current film thickness measuringapparatus is affected directly by variations in the state of anundercoat formed in the precedent step resulting in errors in themeasured values of the film thickness. It is therefore difficult to setaccurately the optimum process conditions based on the measurements ofthe film thickness.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a controlling methodof forming a thin film, and a system for the method, which reducesvariations in the settings of process conditions for the above-mentionedmanufacturing processes and to ensure stability in the formation andtreatment of a thin film.

It is another object of the present invention to provide an exposuremethod and system therefor to constantly a pattern size irrespective ofvariations in the process conditions.

The above objects can be attained by measuring an optical property of anundercoat prior to formation and treatment of a desired thin film, andcorrecting the measurements of the optical property obtained during orafter the formation or treatment of the thin film, thereby controllingthe process conditions accurately.

For instance, in an exposure step for projecting a pattern onto aphotoresist, which is a light-transmitting thin film with a complexrefraction index (the optical property of interest here) varied duringformation and treatment of the thin film, an optimum exposure energy forobtaining a required pattern size is obtainable by measuring the opticalproperty of an undercoat before application of the photoresist,measuring the variation in the optical property due to exposure of awafer coated with the photoresist, and determining the variation in theoptical property of the photoresist.

As exposure of a photoresist proceeds, the optical properties of thephotoresist, such as absorption coefficient (κ) and refractive index(n), are varied as shown in FIGS. 5a and 5b. The manner by which theoptical properties are varied with time depend on, for instance,variations in the reflectivity of the undercoat arising from variationsin process conditions of the manufacturing apparatus in the steppreceding the exposure step. However, the optical properties, such asabsorption coefficient and refractive index, of the photoresist uponcompletion of the projection of the pattern on the wafer aresubstantially constant. As seen in FIGS. 5a and 5b, though the optimumtime to finish exposure varies from T₁ through T₂ to T₃ under theinfluence of variations in the process conditions, the absorptioncoefficient κ₁ and refractive index n₁ upon completion of the exposureare substantially constant. In view of this fact, the variations of theoptical properties, such as absorption coefficient (κ) and refractiveindex (n), of the photoresist with time during exposure can bedetermined by measuring the variations in these optical propertiesduring provisional exposure conducted over part of a photoresist-coatedwafer prior to the pattern projecting step.

The optical properties of the photoresist cannot be measured directly.The values of these properties are obtained by measuring the opticalproperties of the undercoat before application of the photoresist. Basedon the measurement results, the complex index of refraction N (=n-i·κ)of the photoresist derived from the variation in the reflectivity R ofthe wafer upon coating with the photoresist is corrected, and thecorrected complex index of refraction N into the absorption coefficient(κ) and the refractive index (n) is reduced. Based on the opticalproperty values thus obtained, art exposure energy T, photoresistcoating conditions (the rotational frequency of a spinner for applyingthe photoresist, the temperature, humidity or gas pressure in thespinner, or the like) or photoresist baking conditions (bakingtemperature or baking time for baking the applied photoresist) necessaryfor the photoresist on the wafer to fulfill the pattern size accuracyrequirements are calculated. The results of the calculation are fed backto an illumination system in a projection aligner used for actualpattern projection, a photoresist coating machine, or the like, wherebystabilization of control of the pattern size is achievable.

Similarly, a method may be adopted in which an exposure energy T,photoresist coating conditions or photoresist baking conditionsnecessary for a photoresist formed on a wafer to fulfill the patternsize accuracy requirements are determined by measuring both the spectraltransmittance of an undercoat before coating with the photoresist andthe variation with time of the spectral transmittance due to exposure ofthe wafer after coating with the photoresist, and calculating thevariation of the spectral transmittance of the photoresist with timebased on the measurement results.

Furthermore, in a step of forming a thin film having alight-transmitting property, for instance, an optimum film formingcondition for obtaining the required formed film thickness is achievablethrough determining the manner in which an optical property of the filmbeing formed varies, based on both the optical properties of theundercoat before film formation and variations in the optical propertiesof the wafer during the film formation.

As a film is formed on a wafer, the reflectivity Rd of the wafer variesas shown in FIG. 6. The manner by which the reflectivity varies isinfluenced by variations in the process conditions of an apparatus usedin the step precedent to the film forming step. When the film formingtime is controlled based on the variation in the reflectivity of thewafer, therefore, the film forming time varies in the range from T₀ toT₁. That is, under varying process conditions, the reflectivity Rdvaries in the range from curve R₀ to curve R₀ ' and, therefore, controlof the film forming time to a time point when a certain reflectivity isobtained will lead to variation in the film forming time from T₀ to T₁,resulting in the corresponding variation in the thickness of the filmformed. When the optical property of the undercoat before film formation(the optical property is a cause of variations in the processconditions) is measured, the relationship between the reflectivity Rd ofthe wafer and the thickness d of the film formed is as shown in FIG. 7;therefore, when the variation in the reflectivity of the wafer duringfilm formation is reduced to the variation in the thickness of the filmbeing formed, by use of the reflectivity of the undercoat measuredbefore the film formation, the relationship between the reflectivity ofthe wafer and the film forming time shown in FIG. 6 can be reduced tothe relationship between the thickness of the film being formed and thefilm forming time. Thus, it is possible by use of the relationships todetermine, on a real-time basis, the thickness of the film being formed.Accordingly, by converting the film forming rate and the formed filmthickness thus obtained into process condition variables it is possibleto stabilize the operation of the apparatus. The upper and lower curvesin FIG. 7 correspond to curve R₀ and curve R₀ ' in FIG. 6, respectively.

As described above, it is possible, by preliminarily measuring anoptical property before formation and treatment of a desired thin filmand correcting the optical property values measured during or after theformation or treatment of the thin film, to control accurately andstabilize the process conditions.

The optical properties of a thin film in a thin film forming andtreating step will now be explained below, taking reflectivity as anexample.

Determination of the optical properties of the thin film in the thinfilm forming and treating step is performed by measuring thereflectivity R of the wafer, before, during and after the formation ortreatment of the thin film on the wafer at the same position. Based onparameters which are given beforehand, such as the complex index ofrefraction n' of the uppermost layer of an undercoat, etc., variationsin the optical properties of the thin film being formed or treated (thethickness d, absorption coefficient κ, or refractive index n of the thinfilm) are determined from the reflectivity R of the wafer using themeasurement results of the reflectivity R' of the undercoat. Variationsin the process conditions can be determined accurately therefrom.

According to Hiroshi Kubota, Hadoh-Kohgaku (Wave Optics), Iwanami ShotenPublishers, Tokyo, the reflectivity R of a light-transmitting thin filmis given by

    R=f(N, n', R', I.sub.2, d)                                 (1)

where N: complex index of refraction of thin film being formed andtreated

    N=n-i·κ

n: refractive index of thin film being formed and treated

κ: absorption coefficient of thin film being formed and treated

n': complex index of refraction of uppermost layer of undercoat beneaththin film being formed and treated

R': reflectivity of undercoat beneath thin film being formed and treated

I₂ : irradiation illumination

d: thickness of thin film being formed and treated

Therefore, if n' and I₂ are measured beforehand, variations with time ofthe optical properties of the thin film being formed and treated can bedetermined accurately, by measuring R' before the formation or treatmentof the thin film and correcting the measurements of variation inreflectivity R with time.

For instance, because the thickness of a photoresist being irradiatedwith exposure light is not changed by the irradiation, preliminarymeasurement of n', I₂ and d in equation (1) and correction ofmeasurements of variation in the reflectivity R make it possible todetermine accurately the variation in the complex index of refraction N(N=n`i·κ) of the photoresist with time, even if the reflectivity of theundercoat is varied due to variations in the process conditions.Therefore, if an exposure energy E₁ =I₂ (illuminance)×T₂ (time)corresponding to such a complex index of refraction N₁ (=n₁ -i·κ₁) ofthe photoresist as to give the required pattern size is determined, theexposure energy E₁ is the optimum exposure energy.

Besides, the optical properties such as absorption coefficient andrefractive index, of the photoresist eventually converge at known, fixedvalues as shown in FIGS. 5a and 5b. Therefore, when the eventuallyconverging reflectivity R is measured for variation in the thickness dof the photoresist film in this condition, based on the relationshiprepresented by equation (1), the film thickness d can be calculatedaccurately from the reflectivity by use of the relationship shown inFIG. 11, without preliminary measurement as mentioned above regardlessof variations in the reflectivity of the undercoat due to variations inthe process conditions.

Meanwhile, the spectral transmittance of a photoresist, before and afterexposure, is generally as shown in FIG. 12. The curvature varies as thereflectivity of the undercoat varies with the process conditions.Therefore, preliminary measurement of the spectral transmittance of theundercoat before coating with the photoresist and correction of themeasurements of the spectral transmittance during the exposure givevariation in the spectral transmittance of the photoresist with time.When the data on a standard pattern of the spectral transmittance to beobtained at the end of exposure is stored beforehand, then the data on astandard pattern of the spectral transmittance actually measured at theend of exposure is compared with the prestored data and the timerequired for the two kinds of data to agree with each other is measured,the optimum exposure energy E [I (illuminance)×T (time)] can bedetermined accurately.

By feedback of the optimum exposure energy thus obtained to a shutteropening and closing circuit in an illumination system for exposing in aprojection aligner, an accurate and stable control of pattern size inthe projection of the pattern intended can be achieved even if thereflectivity of the undercoat is varied due to variations in the processconditions.

It is known that the thickness of a photoresist film, the initialabsorption coefficient thereof and the like vary from wafer to wafer orfrom lot to lot due to the instability of process conditions. It ispossible, however, to stabilize the photoresist coating step ifcorrection of the measurements of variations in the optical propertiesis carried out through partial exposure of the photoresist at a locationon a scribed line or the like of the wafer by the above-mentioned methodand the corrected values are fed back to a spinning step or a bakingstep so as to yield a constant result. This procedure enables a furtherreduction of variations in the pattern size arising from variations inthe process conditions.

On the other hand, where the thin film to be formed and treated is onewhich is formed and treated by a film forming apparatus, an etchingapparatus or a thin film forming apparatus other than the photoresistcoating machine, the complex index of refraction N (=n-i·κ) of the thinfilm is varied during the formation or treatment. Therefore, it ispossible to determine the variation with time of the thickness d of thethin film being formed and treated from equation (1) by preliminarilymeasuring n' I₂ and N, measuring the reflectivity R' of the wafer beforethe formation and treatment of the thin film, and correcting themeasurements of variation of the reflectivity R with time during theformation and treatment of the thin film. Accordingly, a feedbackcontrol of the process conditions of the forming and treating apparatussuch as to make constant the film thickness determined in theabove-mentioned manner ensures stabilization of the forming and treatingapparatus, even if the reflectivity of the wafer before the formationand treatment of the thin film is varied due to variations in theprocess conditions.

The optical property measuring method is applicable further totransmittance, polarization property, or the like. With the method it isalso possible to determine the variations in the process conditionsaccurately through correction similar to the above-mentioned correctionof reflectivity values. Moreover, it is possible to stabilize theforming and treating apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the general construction of acontrolling system for forming a thin film according to one embodimentof the present invention;

FIG. 2a is an illustration of the condition of multiple reflection in aphotoresist and an undercoat forming film having a light transmittingproperty;

FIG. 2b is a sectional view showing the shape of a photoresist filmdeveloped after .exposure shown in FIG. 2a;

FIG. 3 is a graph showing the manner in which pattern size varies withthe thickness of a photoresist film due to a stationary wave effect;

FIG. 4 is a flow sheet of a step of forming a thin film of apredetermined shape by photoetching;

FIG. 5a is a graph showing the relationship between the absorptioncoefficient κof a photoresist and exposure time, namely, accumulatedexposure energy;

FIG. 5b is a graph showing the relationship between the refractive indexn of the photoresist and exposure time, namely, accumulated exposureenergy;

FIG. 6 is a graph showing the relationship between the reflectivity Rdof a wafer and time required for forming a film on the wafer;

FIG. 7 is a graph showing the relationship between the reflectivity Rdof a wafer and the thickness of a film on the wafer;

FIG. 8 is a block diagram showing the general construction of acontrolling system for forming a thin film according to anotherembodiment of the present invention;

FIG. 9 is a block diagram showing the general construction of acontrolling system for forming a thin film according to a furtherembodiment of the present invention;

FIG. 10 is a schematic illustration of one embodiment of a practicalform of an optical property measuring system which is usable for acontrolling system for forming a thin film according to the presentinvention;

FIG. 11 is a graph showing the relationship between the reflectivityR.sub.∞ of a photoresist subjected to continuing exposure until thereflectivity converges at a fixed value and the thickness of thephotoresist film;

FIG. 12 is a graph showing the variation in spectral transmittance of aphotoresist due to exposure;

FIG. 13 is a schematic illustration of another embodiment of the opticalproperty measuring system in the present invention;

FIG. 14 is a schematic illustration of a further embodiment of theoptical property measuring system in the present invention;

FIG. 15 is a schematic illustration of a controlling system for forminga thin film according to yet another embodiment of the presentinvention;

FIG. 16 is a schematic illustration of yet another embodiment of theoptical property measuring system in the present invention;

FIG. 17 is a block diagram showing the general construction of acontrolling system for forming a thin film according to a still furtherembodiment of the present invention; and

FIG. 18 is a block diagram showing the general construction of acontrolling system for forming a thin film according to an additionalembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some preferred embodiments of the present invention will now beexplained while referring to the accompanying drawings.

EXAMPLE 1

FIG. 1 is a block diagram showing a controlling system for forming athin film according to a first embodiment of the present invention. Inthe figure, a wafer fed along a path for transferring wafers 104 to anoptical property measuring system 108 is subjected to measurement ofoptical property before a thin film is formed and treated thereon. Theresult of the measurement is sent through an interface 103 to a processcontrolling system 45. The wafer to an apparatus for forming andtreating a thin film 107. The wafer is then fed to an optical propertymeasuring system 56. The optical property is measured at the sameposition as that measured by the optical property measuring system 108.The result of the measurement is sent through an interface 101 to theprocess controlling system 45, where the measurement result is correctedaccording to data sent from the optical property measuring system 108.From the data thus obtained through correction, variations in processconditions are calculated. The calculated variations in processconditions are fed back through an interface 102 to the apparatus forforming and treating a thin film 107, thereby stabilizing of theapparatus for forming and treating a thin film.

In this embodiment, the optical property measuring system 108 and theoptical property measuring system 56 can be connected to a plurality ofapparatuses for forming a thin film for which stabilization of thin filmforming and treating conditions is contrived.

The apparatus for forming and treating a thin film 107 in thisembodiment may be a photoresist coating machine. The variations inprocess conditions to be calculated by the process controlling system 45may be variations in the photoresist coating and baking conditions. Theapparatus for forming and treating a thin film 107 may be an etchingapparatus. Furthermore, the apparatus for forming and treating a thinfilm in this embodiment may be a thin film coating apparatus which isnot varied in optical property even when irradiated with light.

EXAMPLE 2

Referring to FIG. 8, there is shown an embodiment in which the apparatusfor forming and treating a thin film is a photoresist coating machine 49and the apparatus to be controlled is a projection aligner. Dataobtained by an optical property measuring system 108 is used by aprocess controlling system 45 for correcting data obtained throughmeasurement by an optical property measuring system 56. The opticalproperty of only the photoresist is extracted from the corrected data,and an optimum exposure energy value for forming a required pattern isestablished based on the extracted optical property data. The exposureenergy value is fed back through an interface 57 to a projection aligner58. When a wafer of which the optical property has been measured by theoptical property measuring systems 108 and 56 is fed into the projectionaligner 58, exposure is carried out with the exposure energy value forthe wafer, so as to stabilize the size of a pattern formed by theprojection aligner 58.

EXAMPLE 3

FIG. 9 shows an embodiment in which the apparatus for forming andtreating a thin film is a photoresist coating machine and the apparatusto be controlled is a developing apparatus. By using data obtained by anoptical property measuring system 108, data obtained on measurement byan optical property measuring system 56 is corrected by a processcontrolling system 45. The optical property of the photoresist only isextracted from the corrected data, and an optimum developing conditionfor forming a required pattern is established according to the extracteddata. The developing condition is fed back to the developing apparatus109 through an interface 110. When a wafer of which the optical propertyhas been measured by the optical property measuring systems 108 and 56is fed into the developing apparatus 109, development is conducted underthe developing condition established for that wafer, thereby stabilizingthe size of a pattern formed by the developing apparatus 109.

EXAMPLE 4

FIG. 10 is a schematic illustration of the optical property measuringsystem 56 in Example 1 and an interface 57. In the figure, illuminatinglight emitted from a light source 26 such as a mercury vapor lamp isguided by a lens 81 to an optical fiber or the like, and is branchedinto two beams of light. The beams of light are led by lenses 82 and 83and pass through shutters 29 and 30. Interference filter 27 permitspassage therethrough of the beam of light with an exposure wavelength.Sharp-cut filter 28 transmits light with a non-exposure wavelength. Thebeams of light are turned ON and OFF by switching the shutters 29 and30. The two beams of light are led through a beamsplitter 31, by whichthe optical axes are combined. The combined beam of light is directedthrough a beamsplitter 85 to irradiate a wafer therewith. A lens 84 isan objective lens. A field stop 55 is provided for narrowing andlimiting the region of irradiation of the wafer with the beam of lighthaving an exposure wavelength. When the shutter 29 is closed and theshutter 30 opened, the wafer is irradiated with the beam of light withnon-exposure wavelengths light is reflected back, transmitted throughthe beamsplitter 85, reflected by a beamsplitter 86 onto an alignmentdetecting system 37. By moving an X-Y stage 36 while under observationof the alignment detecting system (television camera) 32 it is possibleto isolate a specified region on the wafer without exposing of thephotoresist. When the stage is stationary and the shutter 29 is openedwhile the shutter 30 is closed, it is possible to irradiate the locationisolated with exposure light.

On the other hand, data on the complex index of refraction n' of anundercoat, irradiation illuminance I₀ detected by an light quantitymeasuring system 35 (described later) and thickness of photoresist filmd is preliminarily measured and inputted into an optimum exposuredetecting system 37. The reflectivity R' of the undercoat ispreliminarily determined by an optical property measuring system 108 andinputted into an optimum exposure detecting system 37. The optimumexposure detecting system 37 calculates the variation with time of thecomplex index of refraction N of the photoresist from theabove-mentioned formula (1), based on the variation in the reflectivityR of the photoresist, which is a secondary optical property duringexposure and measured by an optical property measuring system(photosensor) 33. An optimum exposure energy E₁ (=exposure time T₂×irradiation illuminance I₂) is obtainable based on the exposure time T₂necessary for the complex index of refraction N of the photoresist toreach a desired value N₁ (=n₁ -i·κ₁) and the irradiation illuminance I₂detected by the light quantity measuring system 35, describedhereinbelow.

The optical properties of the photoresist eventually converges at fixedvalues κ₂₈ and n.sub.∞, as shown in FIGS. 5a and 5b. On the basis of therelationship represented by the formula (1) (wherein N.sub.∞ =n.sub.∞-i·κ.sub.∞ has a known value), therefore, the variation in reflectivityR.sub.∞ with the thickness of photoresist film d in this condition is asshown in FIG. 11. Thus, by exposing a photoresist and measuring thereflectivity R.sub.∞ at the moment the optical property converges at acertain value, it is possible to determine the thickness of photoresistfilm d from the reflectivity according to the relationship shown in FIG.11, without the above-mentioned preliminary measurement. It isaccordingly possible to determine the thickness of photoresist film dfrom the variation in the reflectivity R of the photoresist, asmentioned above, without need for preliminary measurement of thethickness of photoresist film. The thickness of photoresist film d thusobtained can be used to calculate the variation with time of the complexindex of refraction N of the photoresist, in an optimum exposuredetecting system 37.

An illuminance detecting apparatus 34 is a photo-electric transducer formeasuring the illuminance at the wafer position. When the illuminancedetecting apparatus 34 is moved to an exposure position (the position atwhich to detect the variation in the reflectivity R of the photoresist)by use of the X-Y stage, the light quantity measuring system 35 iscapable of measure the illuminance of the exposure light (irradiationilluminance) based on a signal obtained from the illuminance detectingapparatus 34. Then, the optimum exposure detecting system 37 calculatesthe variation with time of the complex index of refraction N of thephotoresist from the data on the complex index of refraction n' of theundercoat, the reflectivity R' of the undercoat, the irradiationilluminance I₂, and the thickness of photoresist film d, and thevariation in the reflectivity R of the photoresist, based on therelationship of the above-mentioned formula (1). The optimum exposuredetecting system 37 determines the optimum exposure energy E₁ (=exposuretime T₂ ×irradiation illuminance I₂) based on the exposure time T₂necessary for the complex index of refraction N of the photoresist toreach a desired value N₁ (=n₁ -i·κ₁) and the irradiation illuminance I₂detected by the illuminance detecting apparatus 34 light quantitymeasuring system 35. The optimum exposure energy E₁ is transferred asdata to an illumination controlling system 38 in a projection aligner58.

In operation, first, a wafer 18 coated with a photoresist is fed intothe apparatus. Then, the shutter 29 is closed. The shutter 30 is openedto irradiate the wafer 18 with non-exposure light. A region on thewafer, for instance, a part of a scribed line is searched with analignment detecting system (television camera) 32 while the wafer 18 ismoved by the X-Y stage 36. At this position, an exposure region islimited by a field stop 55. The shutter 30 is closed. The shutter 29 isopened, and the wafer 18 is exposed to light with an exposurewavelength. The variation in the reflectivity R of the photoresist,which is the secondary optical property of the wafer during exposure, ismeasured by the optical property measuring system (photosensor) 33. Theoptimum exposure detecting system 37 calculates the variation with timeof the complex index of refraction N of the photoresist from the data onthe complex index of refraction n' of the undercoat previously measured,the reflectivity R' of the undercoat, the irradiation illuminance I₂,the thickness of photoresist film d, and the variation in thereflectivity R of the photoresist measured by the optical propertymeasuring system (photosensor) 33, in accordance with theabove-mentioned formula (1). Then, the optimum exposure time T₂ forcomplex index of refraction N of the photoresist to reach the desiredvalue N₁ (=n₁ - i·κ₁), namely, for exposure of the wafer 18 is obtained.Next, the illuminance detecting apparatus 34 is moved to the exposureposition by the X-Y 36. There the illuminance of the exposure light isobtained from the light quantity measuring system 35 through detectionby the illuminance detecting apparatus 34. Thus, the optimum exposuredetecting system 37 determines the optimum exposure energy E₁ (=exposuretime T₂ ×irradiation illuminance I₂) and transfers the optimum exposureenergy E₁ to the projection aligner 58. When the wafer 18, for which theoptimum exposure energy E₁ has been determined, is fed into theprojection aligner 58, an exposure time T₁ according to the energy isestablished by the illumination controlling system 38 based on theexposure light illuminance I₁ detected by an exposure light illuminancedetecting apparatus (not shown in FIG. 10, but denoted by 9 in FIG. 9)disposed in the projection aligner 58. The shutter in the illuminationsystem for exposure 39 is then driven.

In this embodiment, the optical property measuring system 56 can beconnected to a plurality of projection aligner to be fed with the wafers18 for which the optimum exposure energy E₁ has been determined, throughan interface 57.

EXAMPLE 5

When a spectroscope is used in place of the photosensor 33 in Example 3,spectral transmittance during the exposure process can be measured as asecondary optical property. In this case, first the shutter 29 is closedand the shutter 30 opened. The wafer 18 is irradiated with non-exposurelight. A region on the wafer, for instance a part of a scribed line issearched with an alignment detecting system (television camera) 32 whilethe wafer 18 is moved by the X-Y stage 36. The exposure region islimited by a field stop 55. The shutter 30 is opened. The shutter 29 isalso opened, and the wafer 18 is exposed to light containing a varietyof wavelength components including exposure light. Then, spectraltransmittance is detected through the spectroscope, the spectraltransmittance being varied with time from a value before exposure to avalue after the exposure, as shown in FIG. 12. Data of the spectraltransmittance after exposure which shows a fixed value (referencespectral transmittance) is preliminarily inputted to the optimumexposure detecting system 37, which compares the variation with time ofthe spectral transmittance detected through the spectroscope with thedata of the spectral transmittance after exposure (reference spectraltransmittance), and determines an optimum exposure time T₂ for thevarying spectral transmittance to accord with the reference spectraltransmittance. Next, the illuminance detecting apparatus 34 is moved tothe exposure position by the X-Y stage 36, and the illuminance of theexposue light is determined by the light quantity measuring system 35.Thus, the optimum exposure detecting system 37 determines the optimumexposure energy E₁ (=exposure time T₂ ×irradiation illuminance I₂) basedon the irradiation illuminance I₂ obtained from the light quantitymeasuring system 35 and the optimum exposure time T₂. The optimumexposure time T₂ is transferred to the illumination controlling system38 in the projection aligner 58. Therefore, as in the above-mentionedexample, when the optimum exposure energy E₁ has been obtained and isfed into the projection aligner 58, an exposure time T₁ according theenergy is set by the illumination controlling system 38 based on theirradiation illuminance I₁ detected by an exposure light illuminancedetecting apparatus (not shown in FIG. 10, but denoted by 9 in FIG. 16)disposed in the projection aligner 58, and the shutter in theillumination system for exposure 39 is driven.

EXAMPLE 6

Modifications of Example 4 are shown in FIGS. 13 and 14, in which thebasic construction is the same as in FIG. 10. In FIG. 13, light withnon-exposure wavelengths used for measurement of the secondary opticalproperty is projected obliquely and is detected obliquely by aphotosensor 33'. By examining the polarization property, reflectivity orthe like in this case, it is possible to measure the optical propertyunder little influence of the undercoat on the measurement. In FIG. 14,the variations in the transmittance or spectral transmittance of thephotoresist on the substrate due to exposure are capable of beingmeasured by use of photosensors 33 and 33'. This process is effective inprojecting a pattern onto a light-transmitting substance 90, such as aglass, of a TFT liquid crystal display or the like.

EXAMPLE 7

An embodiment in which, unlike the above embodiments, the apparatuscontrolled by an optical property measuring system 56 is a photoresistcoating machine 49 is illustrated in FIG. 15. Data is sent from aprocess controlling system 45 to an interface 102 so that the variationin the optical property measured by the optical property measuringsystem 56 will be constant. The rotating frequency of a spinner 41, thetemperature in a baking furnace 42 or baking time is controlled, wherebyit is possible to stabilize a photoresist coating step. In thisembodiment, the optical property measuring system 56 can be connectedthrough an interface 57 to a plurality of photoresist coating machinesof which the photoresist coating steps are to be stabilized. 40 is awafer stocker.

It is also possible to control both the projection aligner 58 and thephotoresist coating machine 49 by use of the optical property measuringsystem 56.

EXAMPLE 8

FIG. 16 shows an embodiment in which a system for measuring thevariation in optical property due to exposure of a wafer is mounted on areduction projection aligner. In the figure, illuminating light from amercury vapor lamp 1 is controlled to have a fixed illuminance by apower supply controlling system 2. On the other hand, the light from themercury vapor lamp 1 is branched to an exposure system and aprealignment system by a beamsplitter 3. The light transmitted throughthe beamsplitter 3 is turned ON and OFF by controlling the opening andclosing times of a shutter 5 by a shutter controlling system 4. In thissystem, only the exposure wavelength is extracted by an interferencefilter 59. The light transmitted through a condenser lens 6 is projectedonto a reticle 7 provided with a required pattern. An image of thereticle is focused on a wafer 18 by a reduction projection lens 8. Onthe other hand, the other light reflected by the beamsplitter 3 isguided to the prealignment system through a field stop 55 by use of anoptical fiber 90 or the like means. The light is led to either asharp-cut filter 12 which transmits only the light with non-exposurewavelengths or to an interference filter 13 which transmits light withexposure wavelengths, by switching the filters 12 and 13. With thesharp-cut filter 12 selected, an alignment pattern on the wafer 18 canbe detected by a prealignment detecting system 32, without exposing thepattern on the photoresist. A condensed beam of light with exposurewavelength can be set on a scribed line position on the wafer 18. Then,the filter is changed over from the sharp-cut filter 12 to theinterference filter 13, whereby partial exposure of the wafer 18 can beperformed, and the region of irradiation with the exposure light can belimited by a field stop 55. The variation with time of the reflectivityR of the photoresist during the exposure process is measured by aphotosensor 33. The optimum exposure detecting system 37 calculates thevariation with time of the complex index of refraction N of thephotoresist from the complex index of refraction n' of the undercoatpreliminarily measured and inputted, the thickness of photoresist filmd, the reflectivity R' of the undercoat measured by the optical propertymeasuring system 108, the reflectivity R of the photoresist measured bythe photosensor 33 and the illuminance I₂ detected through the lightquantity measuring system 35 supplied with an output from an illuminancedetecting apparatus 9, based on the above-mentioned formula (1). Anoptimum exposure time T₂ for the complex index of refraction N of thephotoresist to reach the desired value N₁ (=n₁ -i·κ₁) is determined, andan optimum exposure energy E₁ is determined based on the optimumexposure time T₂ and the illuminance I₂ detected through the lightquantity measuring system 35. An exposure light illuminance I₂ at thetime of actually projecting a circuit pattern in a reticle 7 through areduction projection lens 8 onto the wafer 18 for which the optimumexposure energy E₁ has been determined is measured by an illuminancedetecting apparatus 9. Then, an exposure illuminance or exposure time T₁for obtaining the optimum exposure energy E₁ is determined based on anexposure light illuminance I₁. The thus obtained data is sent through aninterface 57 to a power supply controlling system 2, which is anilluminance controlling system, and to control the opening and closingtimes of shutters by a shutter controlling system 4, in the same manneras in the above embodiments. The illuminance detecting apparatus 9 is aphoto-electric transducer for measuring the illuminance at the imageforming position, and the illuminance is measured by the light quantitymeasuring system 35. The illuminance detecting apparatus 9 is capable ofmeasure the illuminance in the prealignment system, by moving an X-Ystage 11.

In this embodiment, it is unnecessary to measure the absoluteilluminance. That is, the illuminance at the exposure position forprojecting a pattern drawn on the reticle 7 onto the wafer 18 isdetected by the illuminance detecting apparatus 9, which is then movedto the position of prealignment, and the illuminance of the light led tothe prealignment system is determined. Then, the optimum exposure timeT₁ at the exposure position for projecting the pattern drawn on thereticle 7 onto the wafer 18 is given by the following formula (2):

    T.sub.1 =(I.sub.2 /I.sub.1)×T.sub.2                  (2)

where I₁ is the illuminance at the exposure position, I₂ is theilluminance at the prealignment position, and T₂ is the optimum exposuretime for the light led to the prealignment system.

Thus, the optimum exposure time T₁ at the exposure position forprojecting the pattern drawn on the reticle 7 onto the wafer 18 isobtainable from the optical property (reflectivity, spectraltransmittance or the like) measured by the optical property measuringsystem (photosensor) 33 in the optimum exposure detecting system 37 andthe illuminance measured by the illuminance detecting apparatus 9. Inorder to provide the exposure time thus determined, a controlling system4 controls the illuminance of a mercury vapor lamp through power sourcecontrol 2 in the illumination system and the opening and closing time ofthe shutter 5, whereby the pattern drawn on the reticle 7 is projectedon the wafer 18 for the optimum exposure time. Thus, the pattern on thereticle 7 can be projected in conformity with the demanded pattern. Inthis embodiment, furthermore, the optimum exposure energy for the waferimmediately before exposure is determined, and there is only a shorttime from the determination of the optimum exposure energy to the actualexposure; therefore, there are few variations in the process conditions.In FIG. 16, 19 is a shutter.

EXAMPLE 9

FIG. 17 shows an embodiment in which an optical property measuringsystem 56 is mounted on a photoresist coating machine 49. The opticalproperty 10 of an undercoat of a wafer 18 is measured by an opticalproperty measuring system 108, and the wafer 18 is fed from a waferstocker 40 through a spinner 41 for applying a photoresist and through abaking furnace 42. Thereafter, variations in the reflectivity of thephotoresist during an exposure process is measured by an opticalproperty measuring system 56. The measurement result obtained from theoptical property measuring system 56 and the measurement result obtainedfrom the optical property measuring system 108 are inputted throughinterfaces 57 and 103 to a process controlling system 45, which controlsvariations in process conditions (e.g., coating weight at the spinner41, baking conditions in the baking furnace 42, etc.).

According to this embodiment, variations in the thickness of photoresistfilm and variations in optical property, such as absorption coefficient,due to variations in the process conditions in the photoresist coatingprocess can be reduced, and the photoresist coating process can bestabilized. Consequently, uniform exposure can be achieved for wafersstabilized in the photoresist coating process.

Though in the above embodiment the complex index of refraction N of thephotoresist is calculated from the reflectivity R of the photoresist, itis apparent that direct measurement of the complex index of refraction Nof the photoresist suffices.

EXAMPLE 10

FIG. 18 is a schematic illustration of a system for stabilizingphotoresist coating, baking and exposure processes, in which theapparatuses for which variations in process conditions are corrected area photoresist coating machine 49 and a projection aligner 58. In thefigure, the wafer is fed to an optical property measuring system 108,whereby the optical property of the wafer uncoated with the photoresistis measured. The resultant data is sent through an interface 103 to aprocess controlling system 45. After the measurement of the opticalproperty, the wafer is fed along a path for transferring wafers 104 intothe photoresist coating machine 49, whereby the photoresist is appliedto the wafer and baked. The wafer coated with the photoresist is fedinto an optical property measuring system 56, where the optical propertyof the wafer is measured by the optical property measuring system 108before the wafer is coated with the photoresist. The thus obtained datais sent through an interface 101 to the process controlling system 45.The data sent from the optical property measuring system 108 is used tocorrect the data sent from the optical property measuring system 56.Based on the results of correction, the process controlling system 45calculates the optimum exposure energy as a process variable for theexposure step and also calculate variations in process conditions forthe photoresist coating step. When the wafer of which the opticalproperty has been measured is fed along the path for transferring wafers104 into the projection aligner 58, the optimum exposure energycorresponding to the wafer is inputted from the process controllingsystem 45 into the projection aligner 58 through an interface 57. Then,exposure is carried out for the optimum exposure time, wherebystabilization of pattern size is contrived. The variations in processconditions for the photoresist coating step obtained by the processcontrolling system 45 are fed back through an interface 102 to thephotoresist coating machine 49, in order to stabilize the photoresistcoating and baking conditions.

In this embodiment, the optical property measuring system 108 and theoptical property measuring system 56 can be connected to a plurality ofphotoresist coating machines to stabilize the photoresist coating andbaking conditions constituting the production process conditions, and toa plurality of projection aligners fed with wafers for which the optimumexposure energy has been determined.

When the exposure, coating and baking conditions are controlled once fora few wafers, an effect on automation of the conventional preliminaryoperation is obtained. Where process conditions in the samemanufacturing apparatus vary on a wafer basis, it is possible to controlthe exposure, coating and baking conditions on wafer basis. Furthermore,where variations in the process conditions within a wafer are important,it is possible to control the exposure condition on a chip basis and tocontrol the coating and baking conditions within the wafer.

In the above embodiment, the optical property measuring system 108 canbe incorporated in the photoresist coating machine 49, and the opticalproperty measuring system 56 can be incorporated in the photoresistcoating machine 49 or the projection aligner 58. When the opticalproperty measuring system 56 is incorporated in the projection aligner58, the optimum exposure energy for a wafer can be set immediatelybefore projecting a pattern onto the wafer by the projection aligner 58.Thus, the period of time from the determination of the optimum exposureenergy to the exposure is so short that there arise no influence ofvariations in the process conditions in the period from the photoresistcoating to the exposure. Moreover, the path for transferring wafers isshort, which has the merits of enhancing the efficiency of the step andsuppressing deposition of foreign matter on the wafer during feeding.

Besides, if the optical property measuring system 56 incorporated in thephotoresist coating machine 49 is the embodiment above, it is possibleto measure the optical property of the photoresist immediately uponbaking and after coating. It is therefore possible to control thevariations in process conditions for the photoresist coating machine 49on a real-time basis.

Throughout the drawings, identical reference numerals indicatesubstantially the same portions.

As has been explained hereinabove, according to the present invention,in a step for forming and treating a light-transmitting thin film on awafer, the optical property of the wafer before the formation andtreatment of the thin film is measured, then the measurement data on theoptical property of the formed and treated thin film is corrected toextract only the data on the thin film formed and treated. Based on themeasurement results, the variations in the variations in processconditions for the forming and treating apparatus are determined andcontrolled, whereby stabilization of the forming and treating apparatuscan be contrived.

What is claimed is:
 1. An exposure system comprising:means for measuringa variation with respect to time in an optical property of a photoresistby irradiating a region on a photoresist-coated substrate with a lightof a known illuminance having an exposure wavelength; means formeasuring a thickness of said photoresist; means for calculating anoptimum exposure energy quantity in accordance with a variation withrespect to time in one of a refractive index (n), an absorptioncoefficient (κ) and a complex refractive index (N) of the photoresistcorresponding to a variation of process conditions obtained bycorrecting for said variation with respect to time in the opticalproperty of the photoresist measured by the optical property measuringmeans in relation to a complex index of refraction (n') and reflectivity(R') of an undercoat and the thickness (d) of the photoresist measuredby the thickness measuring means; means for controlling an exposureenergy quantity based on the optimum exposure energy quantity calculatedby the optimum exposure energy calculating means; and, means forexposing the photoresist-coated substrate in accordance with theexposure energy quantity controlled by the controlling means.
 2. Theexposure system as set forth in claim 1, wherein the controlling meanscomprises means for controlling the opening and closing of a shutter inan optical system for illumination.
 3. The exposure system as set forthin claim 1, wherein the measuring means includes means for measuring thevariation with respect to time in the optical property by measuring atleast one of reflectivity, transmittance and polarization property ofthe photoresist.
 4. An exposure system comprising:means for measuring avariation in an optical property of a photoresist with respect to timeby irradiating a region on a photoresist-coated substrate with a lightof a known illuminance having an exposure wavelength and at least oneother light having a wavelength different from the exposure wavelength;means for calculating an optimum exposure energy quantity based on thevariation in the optical property of the photoresist measured by themeasuring means; means for controlling an exposure energy quantity basedon the optimum exposure energy quantity calculated by the optimumexposure energy calculating means; and, means for exposing thephotoresist-coated substrate in accordance with the exposure energyquantity controlled by the controlling means.
 5. An exposure systemcomprising:means for measuring a variation in an optical property of aphotoresist with respect to time by irradiating a region on aphotoresist-coated substrate with a light of a known illuminance havingan exposure wavelength and for measuring thickness of a photoresist filmbased on a difference between the optical property of the photoresistbefore exposure and the optical property of the photoresist after theexposure; means for calculating an optimum exposure energy quantitybased on the variation in the optical property of the photoresistmeasured by the measuring means; means for controlling an exposureenergy quantity based on the optimum exposure energy quantity calculatedby the optimum exposure energy calculating means; and, means forexposing the photoresist-coated substrate in accordance with theexposure energy quantity controlled by the controlling means.
 6. Theexposure system as set forth in claim 1, wherein said thicknessmeasuring means provides means for measuring the thickness of thephotoresist by the optical property of the photoresist.
 7. An exposuresystem comprising:means for measuring a variation in an optical propertyof a photoresist with respect to time by irradiating a region on aphotoresist-coated first substrate with a light of a known illuminancehaving an exposure wavelength; means for calculating at least one of anoptimum photoresist coating condition and baking condition based on thevariation in the optical property of the photoresist measured by themeasuring means; means for controlling at least one of the coatingcondition for coating a second substrate with the photoresist and thebaking condition for baking the photoresist on the substrate based onthe optimum coating or baking condition calculated by the optimumcoating or baking condition calculating means; and, means for exposingthe second substrate controlled by the controlling means.
 8. Theexposure system as set forth in claim 7, wherein the controlling meansis a photoresist coating machine.
 9. The exposure system as set forth inclaim 7, wherein the measuring means includes means for measuring thevariation in the optical property with respect to time by measuring atleast one of the reflectivity, refractive index, transmittance,polarization property and absorption coefficient of the photoresist. 10.The exposure system as set forth in claim 7, wherein the measuring meansincludes means for measuring the variation in the optical property withrespect to time by use of the light having the exposure wavelength andat least one other light having a wavelength different from the exposurewavelength.
 11. The exposure system as set forth in claim 7, wherein themeasuring means includes means for measuring thickness of a photoresistfilm based on a difference between the optical property of thephotoresist before exposure and the optical property of the photoresistafter the exposure.
 12. An exposure system comprising:means forcalculating a variation with respect to time in at least one of arefractive index (n), an absorption coefficient (κ) and a complexrefractive index (N) of a photoresist corresponding to a variation ofprocess conditions; means for calculating an optimum exposure energyquantity so that the variation with respect to time in at least one ofthe refractive index (n), the absorption coefficient (κ) and the complexrefractive index (N) of the photoresist calculated by said calculatingmeans is obtained; means for controlling an exposure energy quantitybased on the optimum exposure energy quantity calculated by the optimumexposure energy calculating means; and means for exposing aphotoresist-coated substrate in accordance with the exposure energyquantity controlled by the controlling means.
 13. The exposure system asset forth in claim 12, wherein said variation calculating means providesmeans for measuring a variation with respect to time in an opticalproperty of a photoresist by irradiating a region on aphotoresist-coated substrate with a light of a known illuminance havingan exposure wavelength to thereby calculate said variation with respectto time in at least one of the refractive index (n), the absorptioncoefficient (κ) and the complex refractive index (N) of the photoresistin accordance with the measured variation with respect to time in theoptical property of the photoresist.
 14. The exposure system as setforth in claim 13, wherein said variation calculating means furtherprovides means for measuring a thickness of said photoresist tocalculate said variation with respect to time in at least one of therefractive index (n), the absorption coefficient (κ) and the complexrefractive index (N) of the photoresist by correcting the variation withrespect to time in the optical property of the photoresist with saidmeasured thickness of the photoresist.
 15. The exposure system as setforth in claim 13, wherein said variation calculating means furtherprovides means for measuring an optical property of an undercoat byirradiating a region on a substrate not yet coated with photoresist witha light of a known illuminance having an exposure wavelength tocalculate said variation with respect to time in at least one of therefractive index (n), the absorption coefficient (κ) and the complexrefractive index (N) of the photoresist by correcting the variation withrespect to time in the optical property of the photoresist with saidmeasured optical property of the undercoat.
 16. An exposure systemcomprising:means for irradiating a region on a substrate not yet coatedwith a photoresist with light of a known illumination having an exposurewavelength to thereby measure an optical property of an undercoat andfor irradiating a region on the substrate coated with the photoresistwith light having an exposure wavelength of a known illuminance tothereby measure the variation in the optical property of the photoresistwith respect to time; means for calculating an optimum exposure energyquantity based on the optical property of the undercoat and thevariation in the optical property of the photoresist with respect totime measured by the measuring means; and, means for controlling thequantity of exposure energy based on the optimum exposure energyquantity calculated by the optimum exposure energy calculating means,and comprises means for projecting a pattern drawn on a photomask ontothe photoresist through control of the quantity of exposure energy bythe controlling means.
 17. The exposure system as set forth in claim 16,wherein the controlling means comprises means for controlling theopening and closing of a shutter in an optical system for illumination.18. An exposure system comprising:means for irradiating a region on asubstrate not yet coated with a photoresist with light of a knownillumination having an exposure wavelength to thereby measure an opticalproperty of an undercoat and for irradiating a region on the substratecoated with the photoresist with the light having the exposurewavelength of the known illuminance to thereby measure a variation inthe optical property of the photoresist with respect to time; means forcalculating an optimum photoresist coating condition based on theoptical property of the undercoat and the variation in the opticalproperty of the photoresist with respect to time measured by themeasuring means; means for controlling a condition for coating thesubstrate with the photoresist based on the optimum coating conditioncalculated by the optimum coating condition calculating means; and,means for projecting a pattern drawn on a photomask onto the substratecontrolled by the controlling means.
 19. The exposure system as setforth in claim 18, wherein the measuring means includes means formeasuring the variation in the optical property with respect to time bymeasuring at least one of reflectivity, a refractive index,transmittance, a polarization property and an absorption coefficient ofthe photoresist.
 20. An exposure system comprising:means for irradiatinga region on a substrate not yet coated with a photoresist with light ofa known illumination having an exposure wavelength to thereby measure anoptical property of an undercoat and for irradiating a region on thesubstrate coated with the photoresist with the light having the exposurewavelength of the known illuminance to thereby measure a variation inthe optical property of the photoresist with respect to time; means forcalculating an optimum photoresist baking condition based on the opticalproperty of the undercoat and the variation in the optical property ofthe photoresist with respect to time measured by the measuring means;means for controlling a condition for baking the substrate with thephotoresist based on the optimum baking condition calculated by theoptimum baking condition calculating means; and means for projecting apattern drawn on a photomask onto the substrate controlled by thecontrolling means.
 21. The exposure system as set forth in claim 20,wherein the measuring means includes means for measuring the variationin the optical property with respect to time by measuring at least oneof the reflectivity, refractive index, transmittance, polarizationproperty and absorption coefficient of the photoresist.
 22. Acontrolling system for treating a thin film comprising:means formeasuring a substrate optical property of a substrate on which a thinfilm having a light-transmitting property is to be treated; means forcalculating accurately a thin film optical property of the treated thinfilm based on the substrate optical property measured by the measuringmeans; means for controlling a condition of an apparatus for treating athin film based on the thin film optical property determined by thecalculating means; and, means for treating the thin film on thesubstrate through controlling the condition by the controlling means.23. An exposure system comprising:means for measuring a variation withrespect to time in a spectral transmittance of a photoresist byirradiating a region on a photoresist-coated substrate with a light of aknown illuminance having an exposure wavelength and at least one otherlight having a wavelength different from the exposure wavelength; meansfor calculating an optimum exposure energy quantity based on a variationwith respect to time in the spectral transmittance of the photoresistmeasured by the measuring means; means for controlling an exposureenergy quantity based on the optimum exposure energy quantity calculatedby the optimum exposure energy calculating means; and, means forexposing the photoresist-coated substrate in accordance with theexposure energy quantity controlled by the controlling means.
 24. Anexposure system comprising:means for measuring an optical property of anundercoat by irradiating a region on a substrate not yet coated withphotoresist with a light of a known illuminance having an exposurewavelength; means for calculating an optimum exposure energy quantity inaccordance with the optical property of the undercoat measured by themeasuring means; means for controlling an exposure energy quantity basedon the optimum exposure energy quantity calculated by the optimumexposure energy calculating means; and means for exposing aphotoresist-coated substrate in accordance with the exposure energyquantity controlled by the controlling means.
 25. An exposure systemcomprising:means for measuring an optical property of an undercoat byirradiating a region on a substrate not yet coated with a photoresistwith a light of a known illuminance having an exposure wavelength andfor measuring a thickness of said photoresist; means for calculating anoptimum exposure energy quantity in accordance with the optical propertyof the undercoat measured and the thickness of said photoresist by themeasuring means; means for controlling an exposure energy quantity basedon the optimum exposure energy quantity calculated by the optimumexposure energy calculating means; and, means for exposing aphotoresist-coated substrate in accordance with the exposure energyquantity controlled by the controlling means.
 26. An exposure systemcomprising:means for measuring a variation with respect to time in anoptical property of a photoresist by irradiating a region on aphotoresist-coated substrate with a light of a known illuminance havingan exposure wavelength; means for measuring a thickness of saidphotoresist; means for calculating an optimum exposure energy quantityin accordance with said variation with respect to time in the opticalproperty of the photoresist measured by the optical property measuringmeans and the thickness of the photoresist measured by the thicknessmeasuring means; means for controlling an exposure energy quantity basedon the optimum exposure energy quantity calculated by the optimumexposure energy calculating means; and means for exposing thephotoresist-coated substrate in accordance with the exposure energyquantity controlled by the controlling means.